Drives for a rotary drum rotating about a horizontal or vaguely oblique axis, and mounted on more than two roller pairs separated by an axial distance relative to each other are known, e.g., from the specification of German patent application No. 2,446,941. Typically at least two individual rollers of the roller pairs are each driven via a hydrostatic motor. However, the drum according to the aforementioned German patent application is only mounted on two roller pairs. Here the rollers roll, as is normally the case, against live rings interspaced on the drum. The torque is transferred from the driven rollers to the live rings by friction.
However, it is a general feature that long drums, particularly rotary kilns, are mounted on more than two roller pairs. As opposed to mounting on two roller pairs, it may then occur that the drum is not in constant contact with all the rollers. This can happen in case of rotary kilns which may distort due to uneven heating of the kiln shell.
If the contact between a drive roller and the drum thus ceases, i.e., the torque with respect to that roller drops to zero, the roller will, as is normal, if it is part of a pressure oil system for all the remaining drive rollers, consume the entire amount of oil, and the drum will come to a standstill, whereas the relieved roller rotates correspondingly faster.
We have invented a drive for a drum which avoids the aforementioned disadvantages of the prior art and makes possible the use of hydrostatically driven rollers also for a drum mounted on more than two roller pairs.